An liquid crystal display (LCD) apparatus includes an LCD panel formed with liquid crystal cells and pixel elements with each associating with a corresponding liquid crystal cell and having a liquid crystal capacitor (hereinafter “CLC”) and a storage capacitor (hereinafter “CST”), a thin film transistor (TFT) electrically coupled with the CLC and CST. These pixel elements are substantially arranged in the form of a matrix having a number of pixel rows and a number of pixel columns. Typically, a plurality of gate signals (scanning signals), generated in response to a horizontal synchronization signal and a vertical synchronization signal, are sequentially applied to the number of pixel rows for sequentially turning on the pixel elements row-by-row. When a gate signal is applied to a pixel row to turn on corresponding TFTs of the pixel elements of a pixel row, a plurality of source signals (data signals) for the pixel row, associated with an image signal to be displayed, are simultaneously applied to the number of pixel columns so as to charge the corresponding CLC and CST of the pixel row for aligning states of the corresponding liquid crystal cells associated with the pixel row to control light transmittance therethrough. By repeating the procedure for all pixel rows, all pixel elements are supplied with corresponding source signals of the image signal, thereby displaying the image signal thereon. The display of the image signal is in generally controlled by the horizontal synchronization signal and the vertical synchronization signal. Typically, in one period of the vertical synchronization signal, all rows are successively scanned once. The number of times a pixel element of a pixel column is scanned in a second is the frequency of the vertical synchronization signal.
Since liquid crystal molecules in the liquid crystal cells themselves do not emit light, an LCD system usually uses a backlight module or a backlight to illuminate the liquid crystal panel so as to produce an image. A backlight includes lamps, such as cold cathode fluorescent lamps (hereinafter “CCFL”), hot cold cathode fluorescent lamps (hereinafter “HCFL”), external electrode fluorescent lamp (hereinafter “EEFL”), or like, for producing light. These lamps are typically powered by a DC-to-AC inverter. The inverter in turn is powered by another power source such as an LCD power supply. The DC-to-AC inverter converts a DC voltage into a high AC voltage (500-2000 V) for driving the lamps, and regulates light-on and light-off times of the lamps for adjusting the brightness of the liquid crystal panel. To reduce interference noises into circuits of the LCD system from the lamps, all lamps are usually driven in the same period and synchronized with each other.
However, interference noises between signals driving the lamps and the horizontal and vertical synchronization signals may exist and generate a so-called “ripple phenomenon” on a screen of the LCD system, which degrades the displaying quality of the LCD system. For example, if a burst mode inverter is used in a conventional LCD system as the DC-to-AC inverter, when the burst signal frequency of the burst mode inverter is equal or near the frequency of the vertical synchronization signal or its harmonics, a large interference noise will be generated periodically. This periodic noise will appear and disappear on the display screen and generate the ripple phenomenon. For instance, if the frequency of the vertical synchronization signal is 60 Hz, when the burst signal frequency of the burst mode inverter is in harmonics of 60 Hz such as 60 Hz, 120 Hz, 180 Hz, 240 Hz . . . , significant noise will result. The burst signal frequency is often preferably set to be about 150 Hz or higher to avoid being close to the harmonics or flicker perceived by human eyes. However, the tolerance of the burst mode frequency could be big due to tolerances of temperature-dependent components, including especially capacitors, the inverter controller IC. Therefore, the burst mode frequency is not as stable as one would like and the ripple phenomenon is very much a concern.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.